Nanotechnology for electrical devices

ABSTRACT

Nanostructured non-stoichiometric non-equilibrium materials are disclosed. Novel electromagnetic materials and their applications are discussed. More specifically, the specifications teach the use of nanotechnology and nanostructured materials for developing novel electrical devices and products.

The present application is a divisional of U.S. patent application Ser.No. 09/274,517 filed Mar. 23, 1999, now U.S. Pat. No. 6,344,271, whichclaims the priority of provisional application No. 60/107,318, filedNov. 6, 1998, entitled “Materials and Products Using NanostructuredNon-stoichiometric Materials,” all of which are assigned to the assigneeof the present invention and which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to non-stoichiometric substances and moreparticularly to nanostructured non-stoichiometric substances andproducts incorporating such substances.

BACKGROUND OF THE INVENTION

Most compounds are prepared as stoichiometric compositions, and numerousmethods of preparing substances for commercial use are motivated inobjective to create stoichiometric compounds. For example, producers oftitania fillers, copper oxide catalysts, titanate dielectrics, ferritemagnetics, carbide tooling products, tin oxide sensors, zinc sulfidephosphors, and gallium nitride electronics all seek stoichiometriccompositions (TiO₂, CuO, BaTiO₃, NiFe₂O₄, TiC, SnO₂, ZnS, and GaN,respectively).

Those skilled in the art will note that conventional powders of oxidesand other compounds, when exposed to reducing atmospheres (e.g.hydrogen, forming gas, ammonia, and others) over a period of time, aretransformed to non-stoichiometric materials. However, the time and costof doing this is very high because the inherent diffusion coefficientsand gas-solid transport phenomena are slow. This has made it difficultand uneconomical to prepare and commercially apply stablenon-stoichiometric forms of materials to useful applications.

Limited benefits of non-stoichiometric materials have been taught byothers; for example, Sukovich and Hutcheson in U.S. Pat. No. 5,798,198teach a non-stoichiometric ferrite carrier. Similarly, Menu in U.S. Pat.No. 5,750,188 teaches a method of forming a thin film ofnon-stoichiometric luminescent zinc oxide. The film is a result of athermodynamically favored defect structure involving non-stoichiometriccompositions where the non-stoichiometric deviation is in parts permillion.

SUMMARY OF THE INVENTION

This invention includes several methods of making non-stoichiometricsubmicron and nanostructured materials and devices from bothstoichiometric and non-stoichiometric precursors. This invention alsoincludes methods of making stoichiometric materials and devices fromnon-stoichiometric precursors. In one aspect, the invention includes animproved sintering technique utilizing submicron non-stoichiometricpowders. The invention also includes a variety of other applications forsubmicron non-stoichiometric materials, including catalysis, photonicdevices, electrical devices and components, magnetic materials anddevices, sensors, biomedical devices, electrochemical products, andenergy and ion conductors.

In one aspect, this invention includes a variety of methods of producinga non-stoichiometric material. According to one method, a submicronpowder of a stoichiometric material is transformed into anon-stoichiometric powder. The submicron powder may also be ananopowder. If desired, the submicron non-stoichiometric powder may besintered into a bulk substance. This invention excludes from its scopethe non-stoichiometry that naturally results from the randomly occurringthermodynamic defects in a bulk crystal of the theoretical stoichiometrywhich are typically on the order of a few hundred parts per million. Asused herein, non-equilibrium means thermodynamic non-equilibrium.

According to another method, a non-stoichiometric submicron material isproduced by quenching a high-temperature vapor of a precursor materialto produce a non-stoichiometric submicron powder. A vapor stream of thehigh temperature vapor flows from an inlet zone, and this stream ispassed through a convergent means to channel the vapor stream through anarea where flow is restricted by controlling the cross-section of theflowing stream. The vapor stream is channeled out of the flowrestriction through a divergent means to an outlet pressure which issmaller than the inlet pressure. This quenches the vapor stream. Theinlet and outlet pressures are maintained, creating a pressuredifferential between them. The pressure differential and thecross-section of the flow restriction are adapted to produce asupersonic flow of the vapor stream. This method may further comprisesintering the resulting powder.

According to yet another method, a nanoscale starting materialcomprising more than one element is provided. At least one of theseelements is an electropositive element. A dopant element with valencydifferent than the electropositive element is added, and the mixture isheated to a selected temperature, preferably greater than the solidstate reaction temperature, for a time sufficient to allow interminglingof the dopant element and the given electropositive element.

According to still another method, two nanopowders are mixed in a ratioselected to produce a desired non-stoichiometric composition. The firstnanopowder comprises a plurality of materials, and the second comprisesa subset of those materials. The materials comprising the firstnanopowder may be metallic, semimetallic, non-metallic, or anycombination thereof. The mixture is heated in a selected atmosphere to atemperature to produce a solid state reaction. The atmosphere mayparticipate in the solid state reaction. This invention also includesthe materials produced via the above methods.

In another aspect, this invention includes a submicronnon-stoichiometric material where the value for a selected physicalproperty of the submicron non-stoichiometric material is greater than10% different from that for a stoichiometric form of the submicronnon-stoichiometric material. Alternately, the relative ratios of thecomponents of the material differ by more than 1% from thestoichiometric values, preferably 2% from the stoichiometric values, andmore preferably 5%. The material maybe a nanomaterial or a nanopowder.

This invention also includes a submicron material wherein a domain sizeof the material is less than 500 nm, and the material isnon-stoichiometric. Preferably, the domain size is less than 100 nm.Alternately, a domain size may be less than 5 times the mean free pathof electrons in the given material, or the mean domain size may be lessthan or equal to a domain size below which the substance exhibits 10% ormore change in at least one property when the domain size is changed bya factor of 2. The material may be a powder or a nanopowder.

In another aspect, this invention includes a method of determining thenon-stoichiometry of a material. A stoichiometric form of the materialand the material whose stoichiometry is to be ascertained (the “unknown”material) are heated separately in a reactive atmosphere to 0.5 timesthe melting point of the material. The weight change per unit sampleweight for the unknown material is monitored. In addition, the weightchange per unit sample weight of the unknown material is compared to theweight change per unit sample weight of the known material.

In another aspect, this invention includes a method of conductingcombinatorial discovery of materials where non-stoichiometric forms ofmaterials are used as precursors.

In another aspect, this invention includes a method of making anon-stoichiometric nanoscale device by fashioning a non-stoichiometricnanoscale material into a device. Alternately, a device is fashionedfrom a stoichiometric material and the stoichiometric material convertedinto a non-stoichiometric form. The stoichiometric material may be anelectrochemical material, a photonic material, or a magnetic material.The non-stoichiometric material may be electroded; and the electrode maycomprise a non-stoichiometric material. This invention also includesstoichiometric devices with non-stoichiometric electrodes. Thenon-stoichiometric materials may further be a nanomaterials.

In another aspect, this invention includes a method of producing astoichiometric material from a non-stoichiometric powder. The powder isprocessed into the shape desired for a stoichiometric material andfurther processed to produce stoichiometric ratios among its components.This invention also includes a method of producing a stoichiometricdevice via the same method.

In another aspect, this invention also includes an improved method ofproducing sintered materials. A submicron stoichiometric powder isformed into a green body. The green body is sintered at a selecteddensification rate and a selected temperature which are lower than thoserequired to sinter larger, stoichiometric powders. This method mayfurther comprise converting the sintered material to a stoichiometricform or stabilizing the non-stoichiometric sintered material by theaddition of a protective coating, secondary phase, or stabilizer. Inthis method, the submicron non-stoichiometric powder may also benanopowders.

This invention also includes a method of producing an improved catalyst.A nanopowder comprising indium tin oxide and alumina are pressed intopellets. The pellets are reduced in a reducing atmosphere to form acatalyst which can promote the formation of hydrogen from 12% methanolvapor at 250° C. This invention also includes the improved catalystprepared by this method.

In another aspect, this invention includes a method of producing animproved photonic material. A high-temperature vapor of a precursormaterial is quenched from a gas stream comprising hydrogen and argon toproduce a non-stoichiometric submicron powder such that the absorptionof selected wavelengths is more than doubled with respect to that of astoichiometric from of the precursor. In this method, the precursormaterial may be stoichiometric ITO; the selected wavelengths would begreater than 500 nm. In addition, this invention includes an improvednon-stoichiometric photonic material produced by this process andexhibiting enhanced absorption of selected wavelengths ofelectromagnetic radiation in comparison to a stoichiometric form of thematerial.

In another aspect, this invention includes a method of producing animproved electric device. Titanium oxide nanopowders are heated in anammonia atmosphere to produce a non-stoichiometric oxynitride oftitanium. The resulting device may also be part of an electricalconductor. This invention also includes the improved electrical deviceproduced by this method.

This invention also includes a variety of methods of making improvedmagnetic materials and devices. According to one method, a nickel zincferrite material is sintered to near theoretical density and heated in areducing atmosphere at an elevated temperature such that the resultingmaterial exhibits higher magnetic loss than the stoichiometric startingmaterial. The atmosphere may comprise 5% H-95% Ar and the temperaturemay be 800° C.

According to another method, a mixture of two stoichiometric nanopowdersis produced from manganese ferrite and nickel zinc ferrite powders.These two powders are pressed together, sintered, and wound. The methodmay further comprise pressing the two nanopowders with a binder,preferably 5% Duramax. This invention also includes the magnetic devicesand materials produced by these methods.

In another aspect, this invention includes methods of making anon-stoichiometric resistor. In one method, the resistor is producedfrom a stoichiometric submicron material and transformed to anon-stoichiometric form. In another method, the resistor is producedfrom non-stoichiometric SiC_(x) nanopowders. The nanopowders aresonicated in polyvinyl alcohol and screened printed on a aluminasubstrate. The resulting resistor element is to produce a resistorhaving a resistance less than 1 megaohm. Platinum or silver dopants maybe added to the sonicated mixture. This invention also includes theimproved resistors produced via these methods and arrays of resistorsproduced via these methods.

In another aspect, this invention also includes a method of producing animproved sensor device. A non-stoichiometric nanopowder is sonicated ina solvent to form a slurry. The slurry is brushed onto screen-printedelectrodes and allowed to dry at to remove the solvent. A dissolvedpolymer may also be included in the slurry. The screen-printedelectrodes may be gold electrodes on an alumina substrate. The screenmay be made from stainless steel mesh at least 8×10 inches in size, witha mesh count of 400, a wire diameter of 0.0007 inches, a bias of 45°,and a polymeric emulsion of 0.0002 inches.

In another aspect, this invention includes an improved sensor deviceprepared from a screen printable paste. A nanopowder and polymer aremechanically mixed; a screen-printing vehicle is added to the mixtureand further mechanically mixed. The mixture is milled and screen-printedonto prepared electrodes. The paste is allowed to level and dry. Thisinvention also includes the improved sensor devices produced by theabove processes.

This invention, in a further aspect, includes a method of making animproved biomedical orthopedic device. A feed powder comprising anon-stoichiometric Ti—Ta—Nb—Zr alloy is milled under non-oxidizingconditions. The milled powder is mixed with a binder dissolved in asolvent and allowed to dry. The mixture is then pressed and incorporatedinto a biomedical device. This invention also includes a biomedicalmaterial comprising a non-stoichiometric submicron powder. In addition,this invention includes a biomedical material produced by this processwherein the powder is a nanopowder.

This invention, in another aspect, includes a method of preparing animproved electronic component. A non-stoichiometric nanoscale materialis mixed with a screen printing material and the resulting pastescreen-painted on an alumina substrate. The paste is wrapped up anddried on a heated plate and further screen-printed with silver-palladiumto form a conducting electrode. The silver-palladium is dried rapidly ona heated plate and the two films co-fired.

In another aspect, this invention includes an improved electrochemicalmaterial comprising a submicron non-stoichiometric material. Thematerial has excess Gibbs free energy in comparison to larger grainedmaterials. In addition, the material exhibits increased solutediffusion, lower phase transformation temperatures, and high compressivetoughness.

In another aspect, this invention includes a method of making animproved energy and ion conducting device. A stoichiometric nanoscalestarting powder is reduced at a temperature between 500° C. and 1200° C.in a forming gas to yield non-stoichiometric nanopowders. The powdersare pressed into discs, sintered, and coated with a cermet pastecomprising equal parts silver and a stoichiometric nanoscale form of thestarting powder. Platinum leads are then attached to the cermet paste.Preferably, the cermet paste comprises silver and a non-stoichiometricversion of the starting powder. The starting powder may beyttria-stabilized cubic zirconia, other metal oxides, a perovskitematerial, or another group IV oxide. This invention also includes theimproved energy and ion conducting device produced by this method. Inaddition, it includes an ion and energy conducting device wherein theion conductor is produced from nanostructured beta alumina, NASICON,lithium nitride, LISICON, silver iodide, Rb₄Cu₁₆I₇Cl₁₃, a polymer, or aperovskite.

In another aspect, this invention includes an improved dopant forsemiconductor materials where the dopant comprises a non-stoichiometricnanocrystalline powder. The grain size of the non-stoichiometricnanocrystalline powder maybe less than 80 nm, preferably 40 nm, and morepreferably 10 nm. The non-stoichiometric nanocrystalline powder mayinclude one or more materials selected from the group comprisingTa_(2/3)O_(0.9), Nb_(2/5)O_(0.74), NiO_(0.98), Mn_(1/2)O_(0.9),Bi_(2/3)O_(0.45), CU_(1.9)O, TiO_(1.1), SiO_(1.55), andV_(2/5)O_(0.975).

BRIEF DESCRIPTION OF THE DRAWING

The invention is described with reference to the several figures of thedrawing, in which,

FIG. 1: UV-Vis absorption spectra of stoichiometric indium tin oxide(yellow) and non-stoichiometric indium tin oxide (blue).

FIG. 2. Resistance of stoichiometric (1) and non-stoichiometric (2)nickel zinc ferrites as a function of frequency.

DETAILED DESCRIPTION

Non-stoichiometric substances in this invention are envisioned assubstances that bridge between the artificial classification ofsubstances—i.e. metals, alloys, oxides, carbides, nitrides, borides,sulfides, chalcogenides, silicides, etc. For example, while tin (Sn) isa metal, tin oxide (SnO₂) is an oxide ceramic. Non-stoichiometric tinoxide is then a form of a substance that transitions the properties ofmetallic tin to ceramic tin oxide. For example, non-stoichiometric tinoxides can be prepared with composition such as SnO_(0.04), SnO_(0.14),SnO_(0.24), SnO_(0.34), SnO_(0.44), SnO_(0.54), SnO_(0.64), SnO_(0.74),SnO_(0.84), and SnO_(0.94). The physical, thermal, chemical, and otherproperties of tin and tin oxide are very different, and the propertiesof non-stoichiometric tin oxide are anticipated to be very different andunique when compared with both metallic tin and ceramic tin oxide. Thepresence of vacancies in SnO_(x) is anticipated to lead to higherconductivities, novel catalytic properties, novel structural properties,novel magnetic properties, faster sintering, and other desirablecommercial performance. A preferred embodiment is to use a submicronnon-stoichiometric form. A more preferred embodiment is to use ananoscale non-stoichiometric form. It is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

Another illustration, without limiting the scope of this invention, isthe non-metal boron and the ceramic boron nitride. In stoichiometricform, boron is B, and the ceramic boron nitride is BN. These twomaterials have very different molecular orbitals and different physical,thermal, chemical, optical, catalytic, structural, and other properties.Additionally, it is easier to process boron than boron nitride.Illustrative but not limiting forms of non-stoichiometric boron nitrideinclude BN_(0.025), BN_(0.125), BN_(0.225), BN_(0.325), BN_(0.425),BN_(0.525), BN_(0.625), BN_(0.725), BN_(0.825), BN_(0.925). It isanticipated that nanoscale forms of these non-stoichiometric BN_(x),will yield novel electrical and electronic properties, novel catalyticproperties, novel structural properties, novel magnetic properties,faster sintering, and other desirable commercial performance. Onceagain, a preferred embodiment is to use a submicron non-stoichiometricform. A more preferred embodiment is to use a nanoscalenon-stoichiometric form. Once again, it is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

Yet another illustration, without limiting the scope of this invention,is metallic titanium and the ceramic titanium carbide. In stoichiometricform, metallic titanium is Ti, and ceramic titanium carbide is TiC.These two materials have very different molecular orbitals and differentphysical, thermal, chemical, optical, catalytic, structural, and otherproperties. It is easier to process metals than ceramics, and theductilities of metals are very different than those of ceramics.Illustrative but not limiting forms of non-stoichiometric titaniumcarbide include TiC_(0.05), TiC_(0.15), TiC_(0.25), TiC_(0.35),TiC_(0.45), TiC_(0.55), TiC_(0.65), TiC_(0.75), TiC_(0.85), TiC_(0.95).It is anticipated that nanoscale forms of nonstoichiometric TiC_(x) willyield novel electrical and electronic properties, novel catalyticproperties, novel structural properties, novel magnetic properties,faster sintering, and other desirable commercial performance. Onceagain, a preferred embodiment is to use a submicron non-stoichiometricform. A more preferred embodiment is to use a nanoscalenon-stoichiometric form. Once again, it is important to note that thenon-stoichiometric form can be converted to a stoichiometric form if andwhen desired. Thus, the beneficial properties of non-stoichiometricforms can be utilized in some applications during processing, whileleaving the flexibility for use of either a stoichiometric or anon-stoichiometric form in the final product.

A further illustration, without limiting the scope of this invention, isthe nickel iron alloy and the ceramic nickel ferrite. In stoichiometricform, nickel iron alloy is NiFe, and ceramic nickel ferrite is NiFe₂O₄.These two materials have very different molecular orbitals and differentphysical, thermal, chemical, optical, catalytic, structural, and otherproperties. It is easier to process alloys than ceramics, and theductilities of alloys are very different than those of ceramics.Illustrative but not limiting forms of non-stoichiometric nickel ferriteinclude NiFe₂O_(3.91), NiFe₂O_(3.71), NiFe₂O_(3.51), NiFe₂O_(3.31),NiFe₂O_(3.11), NiFe₂O_(2.91), NiFe₂O_(2.71), NiFe₂O_(2.51),NiFe₂O_(2.31), NiFe₂O_(2.11), NiFe₂O_(1.91), NiFe₂O_(1.71),NiFe₂O_(1.51), NiFe₂O_(1.31), NiFe₂O_(1.11), NiFe₂O_(0.91),NiFe₂O_(0.71), NiFe₂O_(0.51), NiFe₂O_(0.31), NiFe₂O_(0.11),NiFe_(1.8)O₄, NiFe_(0.8)O₄, Ni_(0.9)Fe₂O_(3.9), Ni_(0.9)Fe₂O₄, andNi_(0.4)Fe₂O₄. It is anticipated that nanoscale forms ofnon-stoichiometric nickel ferrite will yield novel electrical andelectronic properties, novel catalytic properties, novel structuralproperties, novel magnetic properties, faster sintering, and otherdesirable commercial performance. Once again, a preferred embodiment isto use a submicron non-stoichiometric form. A more preferred embodimentis to use a nanoscale non-stoichiometric form. Once again, it isimportant to note that the non-stoichiometric form can be converted to astoichiometric form if and when desired. Thus, the beneficial propertiesof non-stoichiometric forms can be utilized in some applications duringprocessing, while leaving the flexibility for use of either astoichiometric or a non-stoichiometric form in the final product.

Nanostructured materials have small grain sizes and high interfacialareas. Nanostructured materials can be prepared by methods such as thosetaught by us in commonly assigned U.S. Pat. No. 5,788,738 and otherssuch as U.S. Pat. Nos. 5,486,675, 5,447,708, 5,407,458, 5,219,804,5,194,128, 5,064,464, all of which are incorporated herein by reference.Relatively high surface area and small grain size makes nanopowderscommercially suitable for processing into non-stoichiometric forms.

The material compositions to be used in the presently claimed inventionare nanostructured non-stoichiometric substances, i.e. materials whosedomain size have been engineered to sub-micron levels, preferably tonanoscale levels (<100 nm) where domain confinement effects becomeobservable, modifying the properties of the materials. The scope of thisinvention excludes non-stoichiometry that results from thermodynamicallyfavored defect structure.

Nanostructured materials (nanomaterials) are a novel class of materialswhose distinguishing feature is that their average grain size or otherdomain size is within a size range where a variety of confinementeffects dramatically change the properties of the material. A propertywill be altered when the entity or mechanism responsible for thatproperty is confined within a space smaller than the critical lengthassociated with that entity or mechanism. Some illustrations of suchproperties include but are not limited to electrical conductivity,dielectric constant, dielectric strength, dielectric loss, polarization,permittivity, critical current, superconductivity, piezoelectricity,mean free path, curie temperature, critical magnetic field,permeability, coercive force, magnetostriction, magnetoresistance, hallcoefficient, BHmax, critical temperature, melting point, boiling point,sublimation point, phase transformation conditions, vapor pressure,anisotropy, adhesion, density, hardness, ductility, elasticity,porosity, strength, toughness, surface roughness, coefficient of thermalexpansion, thermal conductivity, specific heat, latent heat, refractiveindex, absorptivity, emissivity, dispersivity, scattering, polarization,acidity, basicity, catalysis, reactivity, energy density, activationenergy, free energy, entropy, frequency factor, environmental benigness,bioactivity, biocompatibility, and thermal and pressure coefficients ofproperties. The importance of nanostructured materials to this inventioncan be illustrated by considering the example of the mean free path ofelectrons, which is a key determinant of a material's resistivity. Themean free path in conventional materials and resistivity are related by:

ρ=mv _(E) /nq ²λ

where,

ρ: resistivity

m: mass of electron

v_(E): Fermi energy

n: number of free electrons per unit volume in material

q: charge of electron

λ: mean free path of electron

This equation assumes that the resistivity in the material is determinedin part by the mean free path of electrons and that the electrons have afree path in the bulk. In nanostructured materials, the domain size isconfined to dimensions less than the mean free path and the electronmeets the interface of the domain before it transverses a path equal tothe mean free path. Thus, if the material's domain size is confirmed toa size less than the mean free path, this equation is no longer valid.In a simplistic model, one could replace λ with the domain size, butthat replacement ignores the fact that confinement can also affect “n”and other fundamental properties. This insight suggests that unusualproperties may be expected from devices prepared from materials with adomain size less than the mean free path of electrons.

While the above argument is discussed in light of mean free path, it isimportant to note that the domain confinement effect can be observedeven when the domain size is somewhat larger than the mean free pathbecause: (a) “mean” free path is a statistical number reflecting a meanof path lengths statistically observed in a given material, and (b) invery finely divided materials, the interface volume is significant andall the free electrons do not see the same space; electrons closer tothe interface interact differently than those localized in the center ofthe domain.

The significance of using nanostructured materials can be furtherappreciated if the conductivity of semiconducting oxides is consideredas shown in the equation for conductivity from hoppingmechanism:σ=P_(a)P_(b)2_(e) ²/ckTv[exp(q/kT)]

where,

σ: conductivity

P_(a), P_(b): probabilities that neighboring sites are occupied bydesirable cations

e: electronic charge

n: frequency factor

k: Boltzmann's constant

T: temperature

q: activation energy

c: unit cell dimension

v: hopping velocity

The frequency factor and activation energy are a strong function of themicrostructure confinement and non-stoichiometry; therefore, theconductivity of the same material can be very different innanostructured non-stoichiometric form when compared with naturallyoccurring bulk crystal form of the substance.

As the phrase is used herein, “nanostructured materials” are consideredto be materials with a domain size less than 5 times the mean free pathof electrons in the given material, preferably less than the mean freepath of electrons. Alternatively, the domain size may be less than 500nanometers, and preferably less than 100 nanometers. Nanostructuredmaterials also include substances with a mean domain size less than orequal to the domain size below which the substance exhibits 10% or morechange in at least one property of the substance when the domain size ischanged by a factor of 2, everything else remaining the same.Furthermore, the term nanostructured materials incorporates zerodimensional, one dimensional, two dimensional, and three dimensionalmaterials.

Nanopowders in this invention are nanostructured materials wherein thedomain size is the powder's grain size. For the scope of the invention,the term nanopowders includes powders with an aspect ratio differentthan one, and more specifically powders that satisfy the relation:10⁰<aspect ratio<10⁶.

Submicron materials in this disclosure are materials with mean grainsize less than 1 micrometer.

Non-stoichiometric materials are metastable materials, which have acomposition that is different than that required for stoichiometricbonding between two or more elements. For example, stoichiometrictitania can be represented as TiO₂ while non-stoichiometric titania canbe represented as TiO_(2−x) (TiO_(1.8) and TiO_(1.3) would be twospecific examples of non-stoichiometric titania). Stoichiometric bondingbetween two or more elements indicates that charge balance is achievedamong the elements. In general, a stoichiometric material is given by:

M _(n) Z _(p)

where, Z can be any element from the p, d, and f groups of the periodictable (illustrations include: C, O, N, B, S, H, Se, Te, In, Sb, Al, Ni,F, P, Cl, Br, I, Si, and Ge). M can be any element that can lower itsfree energy by chemically bonding with Z (illustrations include: Ti, Mn,Fe, Ni, Zn, Cu, Sr, Y, Zr, Ta, W, Sc, V, Co, In, Li, Hf, Nb, Mo, Sn, Sb,Al, Ce, Pr, Be, Np, Pa, Gd, Dy, Os, Pt, Pd, Ag, Eu, Er, Yb, Ba, Ga, Cs,Na, K, Mg, Pm, Pr, Ni, Bi, Tl, Ir, Rb, Ca, La, Ac, Re, Hg, Cd, As, Th,Nd, Tb, Md, and Au), where n and p, integers for stoichiometric bondingbetween M and Z, are greater than or equal to 1.

A non-stoichiometric form of the same material may then be given by:

M _(nx) Z _(py)

where 0<x<n and 0<y<p.

An alternative representation of anon-stoichiometric material isM_(n/p)Z_(1−x), where 0<x<1. In this invention, the preferred rangeincludes 0.01<x<0.99, preferably 0.02<x<0.98, and more preferably0.05<x<0.95.

Empirical methods may also be used to determine whether a material isnon-stoichiometric. Some embodiments of such methods are as follows:

1. Heat a stoichiometric form of the material and the material beingevaluated for non-stoichiometry separately in a reactive atmosphere(e.g., oxygen, if oxygen non-stoichiometry is being ascertained) to 0.5times the melting point of the material; monitor the weight change perunit sample weight. The material being evaluated is non-stoichiometricif its weight change per unit sample weight is greater than either 1% ofthe weight of the sample or 25% of the weight change in the sample ofstoichiometric form.

2. Alternatively, perform a quantitative elemental analysis on thematerial; if the relative ratio of the elements yields an “x” that isnot an integer (and the relative ratio deviates by more than 1%,preferably more than 2% and more preferably by more than 5%), thematerial is non-stoichiometric.

3. Alternatively, measure the properties of the material in the idealstoichiometric form and compare this with the substance being evaluatedfor non-stoichiometry; if any property of the material, or thetemperature coefficient of any property varies by more than 10% betweenthe two substances, everything else remaining the same, the substancebeing evaluated is non-stoichiometric.

These empirical methods will not work universally and may givemisleading results because some materials decompose with heating, andanalytical techniques are prone to statistical errors. These empiricalmethods should not be considered limiting and other methods ofestablishing “x” fall within the scope of the invention.

In the M_(n−x)Z_(p−y) representation discussed above, non-stoichiometricmaterials may have more than one “M,” more than one “Z,” or both. Inthis case, the representation can be Π_(I,j)(M_(I,ni−xi)Z_(j,pj,yj)),where Π_(I,j) represents a multiplicity in i and j. A material is thennon-stoichiometric if the relative ratio of any M or any Z or anycombination is different by more than 2.5% than what is needed fortheoretical bonding between the elements. Some illustrations of this,without limiting the scope of the invention, would be non-stoichiometriccompositions such as BaTiO_(3−x), Ba_(1−x)TiO₃, NiFe₂O_(3−x),Ni_(1−x)Fe₂O₃, NiFe₂O₃N_(1−x), PbZrTiO_(3−x), TiCN_(1−x), andTiC_(1−x)N. It is also important to note that, for the scope of thisinvention, non-stoichiometric substances include substances producedwhen one or more of Z and/or M in Π_(I,j)(M_(I,n1−x1)Z_(j,pj,yj)) isreplaced partially or completely with additional elements, i. e., Z_(s)or M_(s). An example of this would be stoichiometric MnFe₂O₄, which,after processing, becomes MnFe₂O_(3.5)N_(0.1) or MnFe₂O_(3.1)B_(0.3).Another example of this is stoichiometric TiB₂ which after processingbecomes TiB_(1.5)N_(0.3) or TiB_(1.1)C_(0.2).

It is important to note that all naturally produced and artificiallyproduced materials have defects because defects are thermodynamicallyfavored. Such thermodynamically favored defects can lead to smallamounts of inherent non-stoichiometry in substances. The presentlyclaimed non-stoichiometric materials differ from such naturally producedand artificially produced substances in the following:

This invention excludes from its scope the non-stoichiometry thatnaturally results from the randomly occurring thermodynamic defects in abulk crystal of the theoretical stoichiometry which are typically on theorder of a few hundred parts per million. As used herein,non-equilibrium means thermodynamic non-equilibrium. Preferred levels ofnon-stoichiometry according to the invention are those whichsignificantly exceed equilibrium levels. Alternatively, the preferredranges include 0.01<x<0.99, preferably 0.02<x<0.98, and more preferably0.05<x<0.95.

This invention teaches the methods for engineering unusualnon-stoichiometric compositions, and provides motivation to harnesstheir unusual properties. The invention stabilizes and makesnon-stoichiometry commercially attractive by engineering nanostructurein the non-stoichiometric material. It should be noted thatnanostructured non-stoichiometric substances are anticipated to haveinterfacial stresses that play an important role in determining theunique properties and unusual thermodynamic nature of these substances,thereby yielding materials with unprecedented compositions of matter andperformance.

In the presently claimed invention, the scope of the invention includesnanostructured materials with a domain size less than 5 times the meanfree path of electrons in the given material, preferably less than themean free path of electrons. In the event that it is difficult totheoretically compute the mean free path of the non-stoichiometricmaterial under consideration, it is recommended that the domain size beless than 500 nanometers, preferably less than 100 nanometers. If it isdifficult to measure the grain size or the grain size changes during theproduction or use of the device, the scope of the invention includesnon-stoichiometric materials with a domain size that exhibit 10% or morechange in at least one property of the substance when the domain size ischanged by a factor of 2, everything else remaining same.

A very wide range of material properties and product performance can beengineered by the practice of the invention. For example, unusual orimproved electrical, electronic, magnetic, optical, electrochemical,chemical, catalytic, thermal, structural, biomedical, surfaceproperties, and combinations thereof can be obtained or varied over awider range using nanostructured non-stoichiometric substances than ispossible using prior art stoichiometric substances. Such benefits canmotivate use of these materials in pellet or film type or multilayertype devices and products.

Nanostructured non-stoichiometric substances can be used as fillers tolower or raise the effective resistivity, effective permittivity, andeffective permeability of a polymer or ceramic matrix. While theseeffects are present at lower loadings, they are expected to be mostpronounced for filler loadings at or above the percolation limit of thefiller in the matrix (i.e. at loadings sufficiently high that electricalcontinuity exists between the filler particles). Other electricalproperties which could potentially be engineered include breakdownvoltage, skin depth, curie temperature, temperature coefficient ofelectrical property, voltage coefficient of electrical property,dissipation factor, work function, band gap, electromagnetic shieldingeffectiveness and degree of radiation hardness. Nanostructurednon-stoichiometric fillers can also be used to engineer magneticproperties such as the coercivity, BH product, hysteresis, and shape ofthe BH curve of a matrix. Even when non-stoichiometric substances areused in monolithic form, these unique electrical, magnetic, andelectronic properties hold significant commercial interest.

Other important characteristics of an optical material are itsrefractive index and transmission and reflection characteristics.Nanostructured non-stoichiometric substances can be used to producecomposites with refractive indices engineered for a particularapplication. Gradient lenses produced from nanostructurednon-stoichiometric composites are anticipated to reduce or eliminate theneed for polishing lenses. The use of nanostructured non-stoichiometricsubstances are anticipated to also help filter specific wavelengths.Furthermore, an expected advantage of nanostructured non-stoichiometricsubstances in optical applications is their enhanced transparencybecause the domain size of nanostructured fillers ranges from about thesame as to more than an order of magnitude less than visible wavelengthsof light. Photonic applications where specific wavelengths of light areprocessed are anticipated to utilize the unique optical properties ofnon-stoichiometric substances.

The high surface area and small grain size of non-stoichiometricsubstances and their composites make them excellent candidates forchemical and electrochemical applications. When used to form electrodesfor electrochemical devices, these materials are expected tosignificantly improve performance, for example, by increasing powerdensity in batteries and reducing minimum operating temperatures forsensors. Nanostructured non-stoichiometric substances are also expectedto modify the chemical properties of composites. These uniquenon-stoichiometric substances are anticipated to be catalytically moreactive and to provide more interface area for interacting with diffusivespecies. They are anticipated to provide the materials needed in ourcommonly assigned U.S. patent application Ser. No. 09/165,439, now U.S.Pat. No. 6,241,195, on a method and process for transforming chemicalspecies which utilizes electromagnetic fields, and which is incorporatedby reference herein. Such substances are anticipated to also modifychemical stability and mobility of diffusing gases. Furthermore,nanostructured non-stoichiometric substances are anticipated to enhancethe chemical properties of propellants and fuels or safety duringstorage and transportation or both.

Many nanostructured non-stoichiometric substances have a domain sizecomparable to the typical mean free path of phonons at moderatetemperatures. These non-stoichiometric substances are anticipated tohave dramatic effects on the thermal conductivity and thermal shockresistance of matrices and products into which they are incorporated.Potential applications include fluids used for heat transfer.

Nanostructured non-stoichiometric substances—which may be utilized incoated and uncoated form—and composites derived thereof are alsoexpected to have significant value in biomedical applications for bothhumans and animals. For example, the small size of nanostructurednon-stoichiometric substances will make them readily transportablethrough pores and capillaries. This suggests that the non-stoichiometricsubstances will be of use in developing novel time-release drugs andmethods of administration and delivery of drugs, markers, and medicalmaterials. A polymer coating can be utilized either to makewater-insoluble fillers into a form that is water soluble, or to makewater-soluble fillers into a form that is water insoluble. A polymercoating on the filler may also be utilized as a means to timedrug-release from a nanoparticle. A polymer coating may further be usedto enable selective filtering, transfer, capture, and removal of speciesand molecules from blood into the nanoparticle.

The invention can be used to prepare propellants and fuels that aresafer to store, transport, process, and use. The non-stoichiometry canalso provide increased energy density or oxidant or both.

The invention can be used to produce superior or more affordablecatalysts for the synthesis of currently used and novel organiccompounds, inorganic compounds, organometallic compounds,pharmaceuticals, polymers, petrochemicals, reagents, metallurgicalproducts, and combinations thereof. The invention can also be used toproduce superior or more affordable catalysts for environmental andother applications that currently or in the future can benefit fromcatalysis. Similarly, the invention can be used to produce superior ormore affordable phosphors for monochromatic and color displayapplications.

A nanoparticulate non-stoichiometric filler for biomedical operationsmight be a carrier or support for a drug of interest, participate in thedrug's functioning, or might even be the drug itself. Possibleadministration routes include oral, topical, and injection routes.Nanoparticulates and nanocomposites are anticipated to also have utilityas markers or as carriers for markers. Their unique properties,including high mobility and unusual physical properties, make themparticularly well-adapted for such tasks.

In some examples of biomedical functions, magnetic non-stoichiometricnanoparticles such as ferrites may be utilized to carry drugs to aregion of interest, where the particles may then be concentrated using amagnetic field. Photocatalytic non-stoichiometric nanoparticles can beutilized to carry drugs to a region of interest and then photoactivated.Thermally sensitive non-stoichiometric nanoparticles can similarly beutilized to transport drugs or markers or species of interest and thenthermally activated in the region of interest. Radioactivenon-stoichiometric nanoparticulate fillers are anticipated to haveutility for chemotherapy. Nanoparticles suitably doped with genetic,cultured, or other biologically active materials may be utilized in asimilar manner to deliver therapy in target areas. Nanocompositeparticles may be used to assist in concentrating the particle and thenproviding therapeutic action. To illustrate, magnetic and photocatalyticnanoparticles may be formed into a composite, administered to a patient,concentrated in area of interest using a magnetic field, and finallyactivated using photons directed to the concentrated particles. Asmarkers, coated or uncoated non-stoichiometric nanoparticulate fillersmay be used for diagnosis of medical conditions. For example, fillersmay be concentrated in a region of the body where they may be viewed bymagnetic resonance imaging or other techniques. In all of theseapplications, the possibility exists that nanoparticulates can bereleased into the body in a controlled fashion over a long time period,by implanting a nanocomposite material having a bioabsorbable matrix,which slowly dissolves in the body and releases its embedded filler.

Other benefits disclosed in our U.S. patent application Ser. No.09/083,893, now U.S. Pat. No. 6,228,904 on nanostructured fillers, andwhich is incorporated by reference herein, are applicable to thenon-stoichiometric materials of the present invention.

Without limiting the scope of this invention, some exemplary methodswhich can be used to produce non-stoichiometric materials, are

Method 1: Start with submicron powders, preferably nanopowders.Transform the powders into a non-stoichiometric form by one or more ofthe following techniques—heating in inert atmosphere, heating inoxidizing atmosphere, heating in reducing atmosphere, solventextraction, chemical reaction, electrochemical transformation,electromagnetic field treatment, ion beam treatment, electron beamtreatment, photonic treatment, rapid quench, plasma treatment, nuclearradiation, supercritical phase treatment, biological treatment, or acombination of one or more techniques. Utilize the non-stoichiometricmaterial so obtained. It may be desirable to sinter thenon-stoichiometric powders into a solid. It may further be desirable toreconvert the non-stoichiometric material to a stoichiometric form.

Method 2: Produce non-stoichiometric powders, preferably nanopowdersdirectly with techniques such as those taught in commonly assigned U.S.Pat. No. 5,788,738. Utilize the non-stoichiometric powders so obtained.For example, sinter and process them as appropriate. Finally, ifdesired, convert them to stoichiometric form.

Method 3: Mix nanoscale powders of a material and at least one of itscomponents in a desired ratio and heat the combination in an inert orother appropriate atmosphere to a temperature that completes the solidstate reaction. The material may comprise metallic, semimetallic, ornon-metallic components, or any combination thereof. It may be possibleto heat the materials in a reactive atmosphere to further control theratio desired among the components in the final product. Utilize thenon-stoichiometric substance so obtained.

Method 4: Add a dopant element with a valency different than one of theelectropositive constituents in the substance in which non-stoichiometryis to be engineered. Heat the mix to a temperature greater than thesolid state reaction temperature for a time that enables interminglingof the dopant element and the primary electropositive constituent. Theobjective in this procedure is to induce non-stoichiometry in a givensubstance because the distribution of secondary element introducesequivalent vacancies in the lattice of the substance.

Optimizing a Non-Stoichiometric Material

This invention enormously multiplies the number of novel substancealternatives available for producing devices and products. A preferredembodiment of this invention is to optimize the composition of thenon-stoichiometric substances for best performance. Such optimizationmay be accomplished by methods known in the art and by parallel searchapproaches such as the combinatorial search method taught by us in U.S.patent application Ser. No. 09/153,418 (abandoned) and by U.S. Pat. No.5,776,359, both of which are incorporated by reference herein. Oneembodiment is to prepare samples of non-stoichiometric materials havingdifferent compositions and to evaluate the properties of the preparedsamples. The material with the best performance is selected as havingthe preferred composition. Another embodiment is to prepare samples ofnon-stoichiometric materials having different compositions, processthese samples into products, and evaluate each product's performance.Finally, the nanostructured non-stoichiometric material composition thatgives the best performing product is selected as the preferredcomposition. In yet another embodiment, a product is prepared from anon-stoichiometric substance and the non-stoichiometry varied in-situuntil the performance of the product is optimized with respect to thedesired specifications. Other methods may be utilized to select the bestcomposition. In all cases, it is important to consider all possibleperformance, environmental, and economic requirements of the productbefore a selection decision is made.

While the above approaches teach how to create and producenon-stoichiometric substances, useful products can be produced fromnanostructured non-stoichiometric substances by techniques and methodsalready known in the art. For example, if a porous body is desired, mixthe non-stoichiometric powders produced as above with an inert materialand reprocess the mixture. As appropriate, add a processing step whichwould remove the inert material using techniques such as dissolution,sublimation, evaporation, leaching, chemical reaction, or biologicalaction. This can lead to a porous body of nanostructured form.

If a given non-stoichiometric material is expensive to prepare, one canmix the non-stoichiometric powders produced as above with astoichiometric material and reprocess the mixture. This may help reducethe processing costs required in conversion from and to stoichiometricform.

One embodiment of this invention is to use non-stoichiometric forms ofmaterials as precursors for combinatorial discovery of materials andrelated technologies such as those disclosed in our commonly assignedU.S. patent application Ser. No. 09/153,418 (abandoned).

Another embodiment of this invention is to prepare devices fromnon-stoichiometric substances. Devices can be prepared using one of themanufacturing methods used currently in the art or a combinationthereof. Examples of processes which can be used at some stage includebut are not limited to pressing, extrusion, molding, screen printing,tape casting, spraying, doctor blading, sputtering, vapor deposition,epitaxy, electrochemical or electrophoretic deposition, thermophoreticdeposition, centrifugal forming, magnetic deposition, and stamping. Thenon-stoichiometric material in the device can be porous or dense, thinor thick, flat or curved, covered with a barrier or exposed. As alreadymentioned, with the motivation of improved performance, stableperformance, reduced costs, or a combination of these,non-stoichiometric materials may be converted partially or completelyinto a stoichiometric form or mixed with stoichiometric materials orboth after being processed into a device.

Another embodiment of this invention is to prepare a device fromstoichiometric materials and then convert the stoichiometric materialsinto a non-stoichiometric form. For example, a ferrite device can beprepared from stoichiometric magnetic materials which can then betransformed, partially or completely, into a non-stoichiometric form byheat treating the device in borane, ammonia, hydrogen, methane, orsilane to form a non-stoichiometric boride, nitride, oxide, hydride,carbide, silicide, or a combination thereof. In another example, asensor or battery device can be prepared from stoichiometricelectrochemical materials which can then be transformed, partially orcompletely, into a non-stoichiometric form by heat treating the devicein borane, ammonia, hydrogen, methane, or silane to form anon-stoichiometric boride, nitride, oxide, hydride, carbide, silicide,or a combination thereof. In a third example, a display device can beprepared from stoichiometric photonic materials which can then betransformed, partially or completely, into a non-stoichiometric form byheat treating the device in borane, ammonia, hydrogen, methane, orsilane to form a non-stoichiometric boride, nitride, oxide, hydride,carbide, silicide, or a combination thereof. In above examples inparticular, and this embodiment in general, the heat treatment can bereplaced by chemical methods, pressure, electrical methods, ionimplantation, or any other method or combination of methods. Inaddition, a substrate maybe incorporated into the device. The substrateon which electrodes are formed can be flat or curved, flexible or rigid,inorganic or organic, thin or thick, porous or dense. The preferredsubstrates are those that provide the mechanical properties needed fordevice life greater than the anticipated device usage life.

In some embodiments of the presently claimed invention, it may bedesirable that the device be electroded. The electrode can be a wire orplate or coil, straight or curved, smooth or rough or wavy, thin orthick, solid or hollow, and flexible or non-flexible. For some devicedesigns, for example, bead/pellet type device designs, it is preferredthat the device is formed directly on the electrode wire or plate orcoil instead of on a substrate. It is important in all cases that theelectrode be conductive and stable at the usage temperatures. It ispreferred that the electrode composition does not react with thenon-stoichiometric substance or the environment during the manufactureor use of the device. The use of nanostructured forms ofnon-stoichiometric materials offers the benefit of sinteringtemperatures for devices which are lower than the sintering temperaturesachievable with coarser grained form. This may enable the use of lowercost electrode materials (e.g., copper or nickel instead of gold orplatinum). It is preferred that the non-stoichiometric form isnon-agglomerated and of a form that favors sintering. It is alsopreferred that the melting point of the electrode is higher than thehighest temperature to be used during the manufacture or use of thedevice. One of ordinary skill in the art will realize that other devicearchitectures can also be used in the presently claimed invention.Furthermore, non-stoichiometric form of electrodes can be utilized toimprove one or more performance parameters of the electrode in thedevice. Some examples of non-stoichiometric electrode substances areNiO_(1−x), NiO_(1−x)N, NiON_(1−x), Cu₂O_(1−x), and PdAgO_(1−x). Themethod described in this specification for preparing non-stoichiometricceramics maybe utilized for preparing non-stoichiometric electrode aswell.

The device can be produced from various non-stoichiometric compositions,including ceramics, metals and alloys, polymers, and composites. Thenon-stoichiometric ceramics include but are not limited to binary,ternary, quaternary, or polyatomic forms of oxides, carbides, nitrides,borides, chalcogenides, halides, silicides, and phosphides. Theinvention also includes non-stoichiometric forms of ceramics, undopedand doped ceramics, and different phases of the same composition.

Metals and alloys such as those formed from a combination of two or moreof s group, p group, d group and f group elements may be utilized. Theinvention includes non-stoichiometric forms of alloys, undoped and dopedmetals and alloys, and different phases of the same composition.Polymers of non-stoichiometric formulations include but are not limitedto those with functional groups that enhance conductivity. Specificexamples include but are not limited to non-stoichiometric compositeswith stoichiometric polymers, defect conducting polymers, and ion-beamtreated polymers. One of ordinary skill in the art will realize thatother polymers, such as metal-filled polymers or conductingceramic-filled polymers, can also be used.

Device miniaturization is also a significant breakthrough that thepresently claimed invention offers through the use of nanostructurednon-stoichiometric materials. Existing precursors that are used toprepare devices are based on micron-sized powders. The mass of thedevice depends in part on the powder size because the device thicknesscannot be less than a few multiples of the precursor powder size. In amultilayer device, each layer cannot be less than a few multiples of theprecursor powder size. With nanostructured powders, the active elementsize and therefore its mass can be reduced significantly. For example,everything else remaining the same, the mass of a device can be reducedby a factor of 1000 if 10 nanometer powders are used instead of 10micron powders. This method of reducing mass and size is relevant todevices in the electronics, electrical, magnetic, telecommunication,biomedical, photonic, sensors, electrochemical, instruments, structural,entertainment, education, display, marker, packaging, thermal, acoustic,and other industries. The presently claimed invention teaches thatnanostructured non-stoichiometric powders are preferred to reduce themass and size of a device.

EXAMPLES Example 1 Processing of Materials

Densification of powders, or sintering, is essentially a process ofremoving the pores between the starting particles, combined with growthand strong bonding between adjacent particles. The driving force fordensification is the free-energy change, or more specifically, thedecrease in surface area and lowering of the free energy.

Among the processing variables that may affect the densificationprocess, the particle size of the starting powder is one of the mostimportant variables. In solid-state processes, assuming that the mattertransport is controlled by lattice diffusion, the volume change of thematerial with respect to time during sintering can be related toprocessing variables as follows:$\frac{\_ V}{V_{o}} = \left\lbrack {3\left( \frac{20\quad \gamma \quad a^{3}D^{o}}{\sqrt{2}{kT}} \right)r^{- 1.2}t^{0.4}} \right\rbrack$

In this equation, V₀ and _V are the initial volume and volume change ofthe target during densification, respectively; T is the sinteringtemperature; t the sintering time; k the Boltzman constant, D⁰ theself-diffusivity, γ the surface energy of the particle, a³ the atomicvolume of the diffusing vacancy, and r the radius of the particle of thestarting powder.

As we can see from the above equation, the sintering time needed toachieve a specific degree of densification is proportional to the cubeof the particle size of the starting powder. Given the same sinteringtemperature and starting material, the densification rate can beincreased drastically by using 100 nm sized powders instead of 10 nmsized powders. Alternatively, to obtain the same densification or toprevent the decomposition of a fragile material at high temperatures,sintering can be conducted at lower temperature with nanostructuredpowders. Thus, nano-sized materials can also significantly decrease thesintering temperatures currently used for micrometer-sized powders. Froma commercial viewpoint, the energy savings from lower processingtemperatures and the reduction of processing times can be substantial.

Another beneficial effect of using nano-sized powders is that, becauseof high surface area and surface diffusivity, nano-sized compositesmaybe sintered without impurity inducing sintering aids, resulting inmore reliable sintered products which exhibit enhanced servicetemperatures and high temperature strength. Other anticipated benefitsdescribed below include commercially attractive processing times andtemperatures, lowered inventory costs, use of lower cost precursors, andthe ability to sinter devices at temperatures that prevent undesirablesecondary reactions or transformations during device fabrication. Whilethis application prefers the use of nanopowders, the teachings hereincan be applied to submicron and larger non-stoichiometric powders.

For example, put the non-stoichiometric material in a die and press thematerial to green densities of 40% or higher. Alternatively, useinjection molding, CIP, HIP, electrophoretic, magnetophoretic, coatings,gel casting, dip coating, precipitation, thick film forming, molding,screen printing, extrusion, and any of techniques known in the art toform a body from the non-stoichiometric nanopowder prepared. Next,sinter the prepared body using a temperature, time, atmosphere, andelectromagnetic field sufficient to reach desired density. If desired,the sintering step may be followed by machining or processing thedensified form as appropriate. Finally, transform the densified andprocessed non-stoichiometric structure to stoichiometric form.

The motivation of this approach is explained above and further includesthe following: The stoichiometric form of M_(n/p)Z_(1−x) may be given byx=0 (i.e. M_(n/p)Z), the lower bound case of the inequality 0<x<1. Whenx=1, we get the upper inequality bound and this represents the pureelement M. It is known to those skilled in the art that the sinteringcharacteristics of M and M_(n/p)Z are very different. Often, M is easierto consolidate and sinter than M_(n/p)Z. Thus, the use of M_(n/p)Z_(1−x)is anticipated to offer performance intermediate to M and M_(n/p)Z. Froma thermodynamic point of view, the unusual interfacial free energies ofnon-stoichiometric forms can allow the use of more commerciallyattractive sintering conditions (i.e. temperature, time, field, andatmosphere) to produce the product of interest. Also, by utilizing thenon-stoichiometric form M_(n/p)Z_(1−x), the unusual properties of thenon-stoichiometric form can be beneficially applied to produce usefulobjects from powders or porous bodies.

For example, in the case of Ti and TiO₂, the sintering temperatures formetal and metal oxide are very different. Metals are easier to sinterand process metals than ceramics. It is expected that the sinteringcharacteristics of a material form intermediate to the two extremes (x=0and x=1) would also be different, in a linear or non-linear manner, thanthe two extremes. It is anticipated that non-stoichiometric forms oftitania will be more reactive, that vacancies will assist pore volumereduction, and that these will reduce the time and temperature needed todensify a structure.

Yet another example would be to use non-stoichiometric forms of doped orundoped superconductors, ferrites, carbides, borides, nitrides, alloys,and oxides, such as NiO, BaTiO₃, ZrO₂, and hafnia. The melting point ofa metal is often less than that of the corresponding ceramic form. Theuse of non-stoichiometric compositions can assist in achieving denseforms at lower temperatures or reduce the time needed to densify amaterial at a given temperature.

In some applications, the unusual properties of non-stoichiometricmaterial may suggest that the device be used in a non-stoichiometricform. However, such devices may change their performance over time orhave other disadvantages. Such problems can be addressed through the useof protective coatings, secondary phases, and stabilizers.

Dense sputtering targets of various compositions can also be preparedusing the above method. These targets can then be used to prepare thinfilms for electronic, information storage, optics, and various otherproducts.

The motivation to use these teachings includes commercially attractiveprocessing times and temperatures, lowered inventory costs, use of lowercost precursors, and the ability to sinter devices at temperatures thatprevent undesirable secondary reactions or transformations during devicefabrication.

Example 2 Catalysis

Nanopowders comprising 75% by weight indium tin oxide (ITO) (mean grainsize: 12.9 nm, 60.9 m²/gm) and 25% by weight alumina (mean grain size:4.6 nm, 56 m²/gm) were mixed and pressed into pellets weighingapproximately 200 mg. The pellet was reduced in a 100 ml/min 5% H-95% Arstream at 300° C. for 10 minutes. The yellow pellet became a bluishgreen color. The pellet was exposed to 12% methanol vapor in air (100ml/min) at about 250° C. and the product gases analyzed using Varian3600 Gas Chromatograph. The gas composition analysis indicated that theproduct gases contained 3400 ppm of hydrogen, suggesting catalyticactivity from the non-stoichiometric blue green pellet. This is incontrast with the observation that the pellet showed no catalyticactivity, every thing else remaining same, when the color was yellow.The blue green pellet was replaced with a platinum wire and thetemperature raised to about 250° C. No catalytic activity was detectablefor the platinum wire at this temperature. These observations suggestthat the non-stoichiometric indium tin oxide has unique and surprisingcatalytic properties when contrasted with stoichiometric indium tinoxide.

Example 3 Photonics and Optics

Stoichiometric ITO (yellow, 30 nm mean grain size) was produced via themethod of commonly assigned U.S. Pat. No. 5,788,738 by feeding ITO inair. Non-stoichiometric ITO (bluish black, 30 nm mean grain size) wasproduced using the method of commonly assigned U.S. Pat. No. 5,788,738by feeding ITO in forming gas (5% hydrogen-95% argon). The nanopowderswere dispersed in water and the UV-Vis absorption spectra were obtainedas shown in FIG. 1.

It was observed that non-stoichiometry more than doubles the absorptionof infrared wavelengths. This experiment suggests that the change instoichiometry can be used to engineer and obtain unusual opticalproperties of a material.

Example 4 Electrical Devices

Titanium oxide nanopowders (white, 25 nm mean grain size) were heated inammonia for 12 hours at 600° C. The nanopowders converted to a deepblue-black color corresponding to non-stoichiometric nanopowder form (28nm mean grain size). The electrical conductivity of thenon-stoichiometric nanopowders was found to be more than ten orders ofmagnitude higher (resistivity of 1.5×10⁻² ohm-cm) than the whitetitanium oxide nanopowders (greater than 10⁸ ohm-cm, which iseffectively insulating). Electron microscopy on the blue-black powdersrevealed that the nanopowders were an oxynitride of titanium (TiON_(x)).It is also of interest to note that commercially availablemicrometer-sized TiN powders exhibit a resistivity of about 1.5 ohm-cm,about two orders of magnitude higher than the non-stoichiometricnanopowder. Thus non-stoichiometry offers unusual non-linear properties.This example suggests the utility of non-stoichiometry and nanostructureto engineer dramatic changes in electrical properties.

Example 5 Magnetic Products

Nanoscale ferrite powders can be heated in ammonia or hydrogen or boraneor methane to form non-stoichiometric ferrite. The powders can then betransformed into a form for incorporation into a device by techniquessuch as extrusion, tape casting, screen printing or any other methods orcombination thereof.

As an illustration, three toroids composed of a nickel zinc ferritematerial were sintered at 900° C. for 2 hours to obtain near-theoreticaldensities. Upon cooling, the toroids were wound with ten turns of 26gauge enamel-coated copper wire. Magnetic properties, includingimpedance, resistance, and serial inductance, were tested from 10 Hz to1 MHz with a Quadtech 7600 LCR meter and from 1 MHz to 1.8 GHz with aHewlett-Packard Model 4291A Analyzer. In each case, measurementconsisted of making a secure contact with the stripped ends of thewindings on the sample toroids and performing a frequency sweep. Oncetested, the three sample toroids were unwound and heated in a reducingatmosphere. Samples were ramped from room temperature to 800° C., heldfor one hour, then allowed to cool. During this cycle, a stream of 5%H-95% Ar flowed continuously over the samples. Upon recovery from thefurnace, a noticeable change in sample color was observed. Previously adark gray, the “reduced” ferrite toroids now had a lighter gray, mottledappearance. The reduced ferrite toroids were rewound with ten turns ofthe same wire and their magnetic properties were re-evaluated. Theobserved results indicated a surprising change in properties in thenon-stoichiometric samples: for a reference frequency of 1 MHz, theresistance increased by 732%, the inductance changed by 12.8%, and theimpedance reduced by 11.4%. That dramatic changes in resistance wereobserved and that the overall impedance of the devices remained largelyunaffected by the non-stoichiometry implies that non-stoichiometry leadsto a corresponding dramatic decrease in inductive reactance. In otherwords, non-stoichiometric ferrite cores exhibit higher magnetic loss.FIG. 2 shows the unusual change in resistance as a function offrequency, suggesting that the non-stoichiometry is changing thefundamental performance of the materials.

Yet another method of producing a magnetic device is as follows: 900 mgof manganese ferrite non-stoichiometric nanopowder and 800 mg of nickelzinc ferrite nanopowder are pressed at 90,000 psi in a quarter inch die.For all powders, 5 wt % Duramax® binder is added prior to pressing forimproved sinterability. Pellets composed of nanopowders are sintered at820° C. for 4 hours in a kiln with a 5° C./min ramping rate.Micrometer-sized reference pellets require sintering temperatures of1200° C. or more for 4 hours, everything else remaining the same. Aftersintering, all pellet diameters are 0.6 cm, and pellet heights are about1 cm. Each pellet is wound with 20 turns of 36 gauge enamel coatedelectrical wire. The final wound pellets are wrapped with Teflon tape toensure that the windings stayed in place. These inductor samples can becharacterized with an Impedance/Gain-phase Analyzer. The performance canbe optimized by varying variables such as the aspect ratio, number ofturns, composition, and grain size.

Example 6 Resistors and Resistor Arrays

Resistors are a mature technology and have served various industries foralmost a century. They are produced in various forms and from varioussubstances. Wire wound resistors are one of the oldest technologies usedin the resistor market. The resistor is made by winding wire onto aceramic bobbin or former. The wire materials are often alloys, and thediameter and length of the wire determine the resistivity. Metal foilresistors are prepared from metal foil that sometimes is less than onemicrometer thick. The foil is stuck on a flat ceramic substrate and theresistance value engineered by precision etching a meandering pattern.These resistors are high value added and exhibit very low temperaturecoefficients of resistance. Film resistors are prepared by vapordeposition, anodization, or plating of metal or cermet or carbon film ona substrate, followed, if needed, by spiral cutting with a diamondwheel. Metal oxide resistors are prepared by depositing oxide vapor.Carbon film resistors are obtained by pyrolysis of hydrocarbon onceramic substrates. Once again, spiraling is commonly used to achievethe desired resistance value. Some resistors are prepared from coatingresistor inks consisting of a glass, metal particle dispersion in aviscous organic binder. The coating is stabilized by firing attemperatures around 600° C. The final resistance value is obtained byspiraling. These techniques are used for preparing discrete resistorchips, networks, or hybrid circuit systems. Desired resistance can befine tuned by air abrasion. Conducting plastic resistors are similar tometal film oxide resistors. They differ in the fact that organic binderis here replaced with a plastic and that the dispersant is often carbon.Sintered structure resistors are prepared by sintering SiC or CrO withsuitable dopants. These resistors are often used as thermistors, not asfixed linear resistors.

The presently claimed invention can be utilized in various embodimentsfor these devices. The composition of existing finished resistors can betransformed into non-stoichiometric forms a variety of techniques, suchas heat treating (400° to 2000° C.) the device in a reducing, oxidizing,nitriding, boronizing, carburizing, or halogenating atmosphere, or acombination of these, over a period of time ranging from a few secondsto hours, shorter times being preferred. Alternatively, existingprocesses to manufacture these devices may be suitably modified at anintermediate stage with one or more different processing steps to yielda non-stoichiometric form. Another embodiment of this invention is toproduce nanopowders of a non-stoichiometric substance and to thensubstitute the substance into existing processes and process it just asone would a stoichiometric substance.

For example, 65 m²/gm SiC_(0.8) nanopowders were produced and sonicatedin polyvinyl alcohol. The resulting dispersion was then screen printedon alumina substrate. After printing, the elements were fired atapproximately 300° C. for a half hour. The resistance of the resultingdevice was less than 1 megaohm. Addition of platinum and silver dopantsreduced the resistance further. Both p-type and n-type behavior wasobserved depending on the dopant.

Arrays are produced by printing multiple elements. The motivation forprinting arrays is to reduce the overall product size and to reduce thecost of placing multiple elements.

Example 7 Sensor Devices

Sensors are components which sense the component's environment orchanges in the component's environment. The environment may include astate of mass, energy, momentum, charge, radiation, field,electrochemistry, biological form, or a combination of one or more ofthese. This example discusses how the teachings in the presently claimedinvention can be utilized to design and practice better performingsensors, including chemical sensors. While the teachings here describe asingle layer thick film, they apply to thing film and multilayerarchitectures as well.

In a chemical sensor, each crystallite of the sensing material has anelectron-depleted surface layer (the so-called space charge layer)having a thickness “L” around it. This length is determined by the Debyelength and the chemisorbed species, and can be approximated by thefollowing expression: $L = {L_{D}\sqrt{\frac{2e\quad V_{s}}{kT}}}$

where,

L_(D): intrinsic value of space charge thickness

eV_(S): height of Schottky barrier at grain boundaries (depends on thesort and amount of adsorbates)

k: Boltzmann's constant

T: temperature

If the crystallite size “D” is greater than twice the space charge layerthickness “L,” which is always true for sensors based on existingmicrometer-size grained stoichiometric materials, the electricalresistance of the sensor device is determined by the electron transportacross each grain boundary, not by the bulk resistance. The resistancein this regime can be expressed as:$R = {R_{o}{\exp \left( \frac{\quad V_{s}}{kT} \right)}}$

where R₀: bulk resistance.

The generally accepted definition of device sensitivity of a device isgiven by (or is a simple variation of):$S = {\frac{R_{g}}{R_{a}} = {\frac{R_{o}{\exp \left( \frac{\quad V_{sg}}{kT} \right)}}{R_{o}{\exp \left( \frac{{V}_{sa}}{kT} \right)}} = {\exp \quad \frac{{\_ V}_{s}}{kT}}}}$

where,

R_(a): resistance of device in air

R_(g): resistance of device in air containing an analyte.

Because “e_V_(S)” is independent of “D” until “D” is greater than twicethe space charge layer thickness “L,” it is no surprise that theobserved sensitivity of the sensor device is independent of crystallitesize in this regime. The above arguments lead to the natural question:what happens when D<2L? In this nanoscale regime, the device resistanceis no longer just grain boundary controlled; instead, the bulkresistance of each grain becomes important. Since, “e_V_(S)” isdependent on the adsorbate type and amount, this change inphenomenological regime provides an unprecedented way to engineerextremely sensitive sensors. In effect, one can engineer the crystallitesize and the non-stoichiometry such that Rg becomes bulk graincontrolled (i.e., very high), while R_(a) remains grain boundarycontrolled (i.e., low). This changes “e_V_(S)” significantly, and sincethe sensitivity “S” depends exponentially on “e_V_(s),” this candramatically enhance the sensitivity of the sensor device. Enhancedsensitivity has been long sought in the sensor industry.

The benefits of nanostructured non-stoichiometric fillers may beexploited in monolithic or composite form. A composite, loosely defined,is a combination of two or more dissimilar materials, or phases,combined in such a way that each material maintains its individualcharacter. The properties of the composite depend greatly on thearrangement of the individual phases present. In completely homogeneouscomposites, the properties tend to be a combination of the properties ofthe distinct phases present, a combination that is often unobtainablewith metals, ceramics, or polymers alone. This makes composites uniqueand very appealing for applications which require a demanding andconflicting matrix of design needs. Sensors are one such applicationwhere conventional materials in monolithic form often excel in meetingsome design goals, but fail to meet others. Composites of nanoscalenon-stoichiometric substances can potentially provide the breakthroughwhere all the needs are simultaneously met. This embodiment isparticularly useful when the selectivity of the sensor needsimprovement.

Sensors (and sensor arrays) can prepared by numerous methods and thebenefits of nanoscale non-stoichiometric substances can be practicedwith any of these methods. In one embodiment, sensing films wereprepared by brushing on a slurry containing nanoscale non-stoichiometricpowders (and polymer, if appropriate) onto a screen-printed electrode ona substrate. The sensor electrodes were prepared using a Presco Model465 Semi-Automatic Screen Printer. This equipment facilitated automaticprinting, with the exception of loading and unloading the substrate. Thescreen used was from Utz Engineering, Inc. The screen was made fromstainless steel mesh and had a frame size of 8×10 inches, a mesh countof 400, a wire diameter of 0.0007 inches, a bias of 45 degrees, and apolymeric emulsion of 0.0002 inches. The gold electrodes were screenprinted on a 96% alumina substrate and then fired in air at 850° C. fora peak time of 12 minutes. Dopant polymers were dissolved in anappropriate solvent. Once the polymer was dissolved, non-stoichiometricnanopowders were added to the solution and sonicated for 20 minutes. Theslurry was then deposited onto an electrode using a small paint brush.Once deposited, the elements were allowed to dry in air at 100° C. for30 minutes to remove the solvent.

In an alternate embodiment, a screen printable paste was first prepared.The paste was again prepared from nanopowder and polymer. Thenanopowder, polymer, and catalyst (when included) were weighed out andmixed together in a mortar and pestle. Next, screen printing vehicle wasweighed out and transferred to the mortar and pestle where the twophases were mixed together. Finally, this paste was placed on a threeroll mill and milled for five minutes. The three roll mill allowed forhigh shear mixing to thoroughly mix the paste and to break upagglomerates in the starting nanopowder. After the paste was prepared itis screen printed on to the prepared electrodes, allowed to level, andthen dried at 100° C. This embodiment illustrates a method for preparingsingle elements and arrays of sensors.

Next, the sensing elements were screened, tested, and optimized forsensitivity, selectivity, and response time, as described below.

The sensitivity is calculated from the change in resistance of thesensor when exposed to a background and when exposed a vapor analytespecies in background and determines the threshold exposure levels. Asimple variation of the above equation describing sensitivity is:${Sensitivity} = \frac{R_{a} - R_{s}}{R_{s}}$

where:

R_(a)=sensor resistance in background

R_(S)=sensor resistance when exposed to analyte vapor.

The selectivity is a comparison of either the sensitivity of anindividual sensor to two different analytes or of two sensors to thesame analyte.${Selectivity} = \frac{{Sensitivity}_{a}}{{Sensitivity}_{b}}$

The response time is the time it takes for the sensor to detect a changein the surrounding environment, defined as the time required for thesensor to reach 90% of its peak resistance (R_(S)).

With non-stoichiometric nanoscale powders, low temperature sensingelements with sensitivity S greater than 1.5, selectivity greater than1.1, and response times less than 10 minutes can be obtained for widerange of gaseous and liquid analytes. With optimization, selectivitygreater than 2, sensitivity greater than 1.5, and response time lessthan 1 minute can be obtained at ambient conditions.

Some specific examples of analytes that can be sensed using theteachings herein, include, but are not limited to: carbon oxides (CO,CO₂), nitrogen oxides (NO_(x)), ammonia, hydrogen sulfide, borane,hydrogen, hydrazine, acidic vapors, alkaline vapors, ozone, oxygen,silane, silicon compounds, halogenated compounds, hydrocarbons, organiccompounds, metallorganic compounds, metal vapors, and volatileinorganics.

Example 8 Biomedical Products

Mechanical alloying can be used to prepare nanocrystallinenon-stoichiometric alloys. The feed powder Ti-4.9Ta-11Nb-15.2Zr isloaded in non-stoichiometric proportions into a cylindrical hardenedsteel vial with hardened steel mill balls. The ball-to-powder ratio ispreferably high (5:1). The loading process is preferably done within anargon atmosphere glove box. The environment inside is maintained at anoxygen concentration of <100 PPM and moisture content of <3.0 PPM. Themill itself is set up outside of the glove box and the vial and millhousing cooled using forced air convection. After milling, the vial istransferred back to the glove box where the non-stoichiometric powder iscollected and submitted for analysis or further processing. To preparean orthopedic implant, the synthesized powders are uniaxially pressed.Poly(ethylene glycol) (PEG) may be used as a binder for compaction ofthe powders. PEG is added to the powders by preparing a 1 weight percentsolution in ethanol and wet mixing the solution with the alloyedpowders. The homogeneous mixture is air dried at room temperature. Apress can be used to compact the powders in a die. A uniaxial 11,250 lb.force is applied (resulting in 225,000 psi of pressure) which isappropriate for implant specimens.

One advantage of non-stoichiometric nanoscale powders is the potentialuse of non-toxic elements in orthopedic and other biomedical implants.In general, biomedical implants are engineered to control propertiessuch as strength, toughness, modulus, corrosion resistance,biocompatibility, porosity, surface roughness, and wear resistance. Thematerials described in the previous paragraph can be optimized to matchthe modulus of bone, a desirable characteristic of materials for somejoint replacement applications. In other embodiments, nanopowders can beutilized for drug delivery and as markers for diagnosis. Nanopowders canalso be utilized for enhancing the solubility of drugs in organic andinorganic solvents. In yet other embodiments, the teachings can beapplied to various products where inorganic and organic powders arecurrently being utilized, as known to those skilled in the art.

Example 9 Electronic Components

Electronic components, for example, disc and multilayer capacitors,inductors, resistors, filters, antennas, piezo devices, LED, sensors,connectors, varistors, thermistors, transformers, current converters,shields, or arrays of such components in conventional mount or surfacemount form, can be prepared using the teachings herein. As an example,to prepare varistors from nanoscale non-stoichiometric materials, apaste of the powders was prepared by mixing the powder and screenprinting vehicle with a glass stir rod. Exemplary compositions includeZnO_(1−x), Bi_(2/3)O, and other oxides. Silver-palladium was used as theconducting electrode material. A screen with a rectangular array patternwas used to print the paste on an alumina substrate. The processconsists of screen printing the electrode and rapidly drying the film ona heated plate. The process was attended and precautions taken toprevent electrically shorting the device. The final electrode wasapplied in the same manner as the first. The effectivenon-stoichiometric nanostructured-filler based composite area in thedevice due to the offset of the electrodes was small (0.2315 cm²).However, this offset may be increased or further decreased to suit theneeds of the application. The thick green films were co-fired at 900° C.for 60 minutes.

Such a device offers a means to control surge voltages. An accuratedetermination of device non-linearity, a, can be obtained using theempirical varistor power law equation:

I=nV ^(α)

where:

I=current.

n=the varistor power coefficient.

V=voltage.

The value of α obtained for the nanostructured non-stoichiometric deviceis anticipated to be 10 fold higher than that achievable withmicrometer-sized stoichiometric fillers. It is also expected that theresistance of the boundaries would be lower, enabling clampingcapability of lower voltages and higher frequencies. Other componentsthat can specifically benefit from the high surface area ofnanostructured non-stoichiometric materials include but are not limitedto positive temperature coefficient resistors and barrier layercapacitors.

Example 10 Electrochemical Products

Electrochemical products, for example, batteries, electrolytic cells,corrosion inhibitors, electrodes in metallurgical applications and otherindustries, pH sensors, and electrochemical sensors, can benefit fromthe use of non-stoichiometric nanopowders. The most distinctive featureof these non-stoichiometric nanopowder materials is their uniquethermodynamic state and the large number of atoms situated in theinterfaces. A 10 nm nanocrystalline metal particle contains typically10²⁵ atoms which are situated on or near the interface per cubic meterof material; thus, 30% of total atoms in the material are situated inthe interfaces or on the surface and exhibit non-bulk properties. Such aunique ultra-fine structure of nanopowders, when applied toelectrochemical products, can lead to a drastic improvement of theirperformance. The ultra-fine (nanometer scale) microstructure ofnanostructured hydrogen storage materials, to illustrate, will not onlyenhance the thermodynamics and kinetics of hydriding and dehydridingprocesses, but also improve their structure stability, and thusreliability and life time.

Particularly, nanostructured materials offer the following motivationfor their utilization:

(i) Drastic Increase of Species Solubility or Capacity

The ultra-fine grain size of nanostructured materials gives an excessGibbs free energy to the system compared to the conventional largegrained (micrometer size) hydrides. This will significantly enhance thesolubility of solute atoms, including hydrogen, because:$\frac{C_{d}}{C_{\infty}} = {\frac{k\quad V}{RT}\frac{\sigma}{d}}$

where:

C_(d) and C_(□)=solubilities of a solute in the material with averagegrain size d and infinite grain size, respectively;

R=gas constant;

T=temperature;

V=the molar volume of the solute;

k=Boltzmann's constant;

σ=the surface energy of the grain.

Thus, theoretically, a 10 nm grained hydride is expected to have ahydrogen solubility 1000 times higher than a 10 μm grained hydride withthe same chemical composition. The use of non-stoichiometric nanoscalepowders offers to further enhance the thermodynamic and/or kineticpotential of the system. Other advantages of non-stoichiometricformulations, for example, faster and more economical processingconditions, still apply.

(ii) Significant Enhancement of Hydrogen Diffusivity

The large volume fraction of interface in nanostructured materials willresult in grain boundary diffusion dominating the overall diffusion inthe materials. The overall or effective diffusivity of solute atoms inthe material is given by:

D ^(eff) =fD _(gb)+(1−f)D _(lt)

where:

D^(eff)=the effective or overall diffusion coefficient;

D_(gb)=the diffusion coefficient in grain boundaries;

D_(lt)=the diffusion coefficient within grains.

f=the fraction of solute atoms on the grain boundaries.

Since D_(gb) normally is 10⁴ times higher than D_(lt), orD_(gb)>>D_(lt), and more than 30% of atoms are situated in the grainboundaries, the above equation can be rewritten as

D ^(eff) ≈fD _(gb)=0.3D _(gb) <<D _(lt)

The solute diffusion coefficient in nanostructured materials, therefore,is expected to be 1000 to 10,000 times higher than in conventionalmicro-grained materials.

(iii) Reduction of Temperature and Pressure for Hydride Formation andDissociation

The excess free Gibbs energy due to the ultra-fine structure ofnanomaterials will also lead to significant change in phasetransformation temperatures such as the hydride formation temperature.The phase transformation temperature change _T due to the ultrafinestructure is related to the grain size d by:${\_ T} = {\frac{\left( {\sigma_{1} - \sigma_{2}} \right)T_{c}}{L}\frac{k}{d}}$

where:

σ₁, σ₂=specific surface energies of phase 1 and phase 2, respectively;

L=the heat of transformation from phase 1 to phase 2;

T_(c)=the phase transformation for the bulk material;

k=Boltzmann's constant.

Thus, the phase transformation temperature is expected to change as thegrain size decreases. Because the hydrogen dissociation pressuredecreases as the dissociation temperature decreases, the ultra-finemicrostructure of nanostructured materials in general, andnon-stoichiometric nanomaterials in particular, is preferable designguideline to a lower hydrogen dissociation pressure. This is verydesirable in hydrogen storage technologies. This basic guideline forpractice applies even to other electrochemical couples and systems suchas batteries and electrodes. The benefits of lower phase transformationtemperature have utility beyond electrochemical products and apply tothermal (e.g. heat transfer fluids) and other applications as well.

(iv) Higher Resistance to Pulverization During Hydriding/DehydridingProcesses

High strength is essential to pulverization resistance due to largelattice expansion and contraction during hydriding/dehydridingprocesses. The ultrafine grain size of nanostructured hydrides offers adrastic improvement in their structure stability. This can be inferredfrom the yield strength of a material which is related to its grain sized by the Hall-Petch relationship:$\sigma_{y} = {\sigma_{o} + \frac{k_{y}}{\sqrt{d}}}$

Fracture toughness, K_(1C), is related to grain size by:

K _(1C)=σ_(y){square root over (πα_(c))}

where:

σ_(y)=the yield strength;

σ_(o)=the frictional stress needed to move the dislocation;

k_(y)=a constant;

a_(c)=the critical crack length.

This indicates that as the grain size decreases from 10 μm to 10 nm,both the strength and fracture toughness are expected to increase by afactor of 30, which in turn leads to a higher resistance topulverization. Thus, electrochemical products in particular, and otherproducts in general, can benefit from superior performance ofnanostructured materials.

Some specific examples for the use of non-stoichiometric nanomaterialsin electrochemical products would be rare-earth doped or undopedMg_(1.8)Ni, Ni—ZrNi_(1.6), La_(1.6)Ni₅, and other existing compositionswith non-stoichiometry as explained previously.

Example 11 Energy and Ion Conducting Devices

Stoichiometric nanoscale 9 mole % yttria-stabilized cubic zircorniapowders (Y₁₈Zr₉₁O₂₀₉) are first reduced at moderate temperatures (500°to 1200° C.) in a forming, or reactive, gas to yield non-stoichiometricY₁₈Zr₉₁O₁₈₅ nanopowders. These powders are pressed into 3 mm diameterdiscs and then sintered to high densities. The disks should bepreferably sintered at low temperatures (preferably 800° C. to 1200° C.)for short times (preferably 6 to 24 hours) to minimize grain growth.These nanopowders, as discussed before, can be readily sintered to fulltheoretical densities (99% or more). Careful control and optimization ofthe sintering profile and time can reduce the sintering temperature andtime further. The two ends of the cylindrical discs so produced are thencoated with a cermet paste consisting of a mix of silver and nanoscalestoichiometric yttria stabilized zirconia powder (a 50—50 wt % mix).Non-stoichiometric nanoscale powders can be utilized in the electrode aswell. Platinum leads are then attached to the cermet layer. This devicecan serve as an oxygen-conducting electrolyte with significantly higheroxygen ion conductivity at lower temperatures than conventionalelectrolytes. Exemplary devices include but are not limited to oxygensensors, oxygen pumps, or fuel cells. In this example, the degree ofnon-stoichiometry is arbitrarily chosen, and further optimization can bebeneficial to the economics and performance.

The benefits of this invention can be utilized even when the yttria inthe zirconia formulation is replaced with other stabilizers such asscandium oxide, calcium oxide, and other oxides. Similarly, other GroupIV oxides (e.g. ceria) and perovskites can be used instead of zirconia.Other ion conductors, for example, beta alumina and NASICONs for sodiumion, lithium nitride and LISICONs for lithium ions, silver iodide forsilver ions, Rb₄Cu₁₆I₇Cl₁₃ for copper ions, polymers such as nafion andperovskites for hydrogen protons, can all benefit from the use ofnon-stoichiometry in the ion conducting electrolytes and/or electrodes.

Example 12 Dopants in Formulations and Inks

Often, it is necessary to add secondary phase particles to a primarypowder element to achieve a desired property, such as temperaturecoefficient of the dielectric constant. For example, commercialcapacitor formulations of the Electronic Industry of America (EIA) X7Rdesignation contain additions of dopants (e.g. tantalum oxide, niobiumoxide, nickel oxide, bismuth oxide, silicates, titanates, and manganeseoxide) which are added to the base barium titanate powder to tailor thetemperature-capacitance or other characteristics of the material. Thesecondary phase particle additions are also often used to facilitate lowtemperature sintering. These materials include, but are not limited to,bismuth oxide, copper oxide, titanium oxide, silicon oxide, and vanadiumoxide.

In these powder mixtures, it is usually desirable to achieve a uniformmixture of the primary phase particles and the secondary phaseparticles. This can be difficult if the volume fraction of the secondaryparticles is small and if the size of the secondary particles is largein relation to that of the primary particles. The problem is that thenumber fraction of the secondary particle phase is small in relation tothat of the primary particle phase; thus, the relative distances betweenthe secondary phase particles can be rather large. This can translate toa non-uniform distribution of the secondary phase particle speciesthroughout the powder element and also in the microstructure of thefinal product.

Nanocrystalline powders in general and non-stoichiometric powders inparticular produced by any technique can reduce the size of thesecondary particles relative to primary particles and in turn, increasethe number fraction of the secondary particles in the powder element.This will translate to a uniform mixedness in the powder element and inthe product's microstructure.

To illustrate, 80 nm (preferably 40 nm, more preferably 10 nm)Ta_(2/3)O_(0.9), Nb_(2/5)O_(0.74), NiO_(0.98), Mn_(1/2)O_(0.9),Bi_(2/3)O_(0.45), Cu_(1.9)O, TiO_(1.1), SiO_(1.55), and V_(2/5)O_(0.975)are examples of non-stoichiometric nanopowders that can be used asdopants in device formulations and inks.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method of modifying the performance of anelectrical device comprising: providing a device prepared fromstoichiometric nanostructured material; converting the stoichiometricnanostructured material into a non-stoichiometric non-equilibriumnanostructured material wherein the act of converting is accomplished byheat treatment of the device in an atmosphere selected from the groupconsisting of: reducing, oxidizing, nitriding, boronizing, carburizing,and halogenating.
 2. The method of claim 1 wherein the nanostructuredmaterial has a domain size less than 500 nm.
 3. The method of claim 1wherein the electrical device comprises a resistor.
 4. The method ofclaim 1 wherein the nanostructured material has a domain size less than100 nm.